Mobile communication system

ABSTRACT

A radio base station includes a mobile communication system, a first relay node and a radio base station connected via a radio bearer, a second relay node and a radio base station connected via a radio bearer, and a mobile station configured to conduct a handover process between a first and second state. In the first state a radio bearer is established with the first relay node in order to communicate via the first relay node and the radio base station. In the second state a radio bearer is established with the second relay node in order to communicate via the second relay node and the radio base station. The mobile station is configured such that control signals are transmitted and received via the radio bearer between the first relay node and the radio base station, via the radio bearer between the second relay node and the radio base station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of the U.S. patentapplication Ser. No. 13/266,479, filed on Oct. 27, 2011, which claimspriority to PCT International Application No. PCT/JP2010/057086, filedon Apr. 21, 2010, which claims priority to Japanese Patent ApplicationNo. 2009-108565, filed on Apr. 27, 2009. The contents of these priorapplications are incorporated herein by reference in their entirety.

BACKGROUND OF INVENTION

1. Technical Field

The present invention relates to a mobile communication system.

2. Background Art

A mobile communication system of the LTE scheme (Release.8) defined bythe 3GPP, as illustrated in FIG. 8, is configured such that when ahandover process by a mobile station UE is carried out from a radio basestation eNB#1 to a radio base station eNB#2, control signals involved inthe handover process are transmitted and received between the radio basestation eNB#1 and the radio base station eNB#2 via an X2 bearer that hasbeen installed between the radio base station eNB#1 and the radio basestation eNB#2.

As illustrated in FIG. 8, the radio base station eNB#1 and the radiobase station eNB #2 include a network layer 1 (NW L1) function, anetwork layer 2 (NW L2) function, an IP (Internet Protocol) layerfunction, and an SCTP (Stream Control Transmission Protocol) layerfunction as the X2 bearer functions for establishing the X2 bearer.

In the LTE-advanced mobile communication system, which is anext-generation communication scheme of the LTE scheme, “relay nodes(RN)” including the same functions as a radio base station eNB canestablish a connection between a mobile station UE and the radio basestation eNB.

However, the conventional mobile communication system has no regulationfor how handover processes by the mobile station UE are to be handledwhen the relay nodes RN have been connected.

SUMMARY OF INVENTION

One or more embodiments of the present invention may provide a mobilecommunication system capable of implementing a handover process by amobile station even when a relay node is connected.

The first feature of the present invention is summarized in that amobile communication system, a first relay node and a radio base stationare connected via a radio bearer, a second relay node and a radio basestation are connected via a radio bearer, a mobile station is configuredso as to conduct a handover process between a first state wherein aradio bearer is established with the first relay node in order tocommunicate via the first relay node and the radio base station, and asecond state wherein a radio bearer is established with the second relaynode in order to communicate via the second relay node and the radiobase station and the mobile station is configured such that in thehandover process, control signals involved in the handover process aretransmitted and received via the radio bearer between the first relaynode and the radio base station, and via the radio bearer between thesecond relay node and the radio base station.

The first feature of the present invention is summarized in that when ameasurement report is received from the mobile station, the first relaynode is configured so as to transfer the measurement report to the radiobase station via the radio bearer between the first relay node and theradio base station and when it is determined based on the measurementreport that a handover process of the mobile station from the firststate to the second state is to be initiated, the radio base station isconfigured so as to transmit a handover request signal givingnotification of the determination as a control signal involved in thehandover process to the second relay node via the radio bearer betweenthe second relay node and the radio base station.

The first feature of the present invention is summarized in that when itis determined that a handover process of the mobile station from thefirst state to the second state is to be initiated, the first relay nodeis configured so as to transmit a handover request signal givingnotification of the determination as a control signal involved in thehandover process to the radio base station via the radio bearer betweenthe first relay node and the radio base station and the radio basestation is configured so as to transfer the received handover requestsignal to the second relay node via the radio bearer between the secondrelay node and the radio base station.

As has been described above, according to the present invention, it ispossible to provide a mobile communication system capable ofimplementing a handover process by a mobile station even when a relaynode is connected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the entire configuration of a mobilecommunication system according to a first embodiment of the presentinvention.

FIG. 2 is a diagram of a protocol stack in the mobile communicationsystem according to the first embodiment of the present invention.

FIG. 3 is a sequence diagram illustrating the operation of the mobilecommunication system according to the first embodiment of the presentinvention.

FIG. 4 is a diagram of the protocol stack in the mobile communicationsystem according to a second embodiment of the present invention.

FIG. 5 is a sequence diagram illustrating the operation of the mobilecommunication system according to the second embodiment of the presentinvention.

FIG. 6 is a diagram of the protocol stack in the mobile communicationsystem according to a third embodiment of the present invention.

FIG. 7 is a sequence diagram illustrating the operation of the mobilecommunication system according to the third embodiment of the presentinvention.

FIG. 8 is a diagram of the protocol stack in a current mobilecommunication system.

DETAILED DESCRIPTION

(Mobile communication system according to a first embodiment of thepresent invention)

In embodiments of the invention, numerous specific details are set forthin order to provide a more thorough understanding of the invention.However, it will be apparent to one with ordinary skill in the art thatthe invention may be practiced without these specific details. In otherinstances, well-known features have not been described in detail toavoid obscuring the invention. With reference to FIG. 1 to FIG. 3, amobile communication system according to the first embodiment of thepresent invention is described.

The mobile communication system according to the present invention is anLTE-Advanced mobile communication system including, for example, asillustrated in FIG. 1, a mobile switching center MME, relay nodes RN1 toRN4, a radio base station DeNB (Donor eNB)1 that is connected to relaynode RN1, a radio base station DeNB2 that is connected to the relaynodes RN2 and RN3, and a radio base station eNB1.

Herein, the radio base station DeNB1 and the radio base station DeNB2are connected via an X2-C interface, and the radio base station DeNB2and the radio base station eNB1 are connected via an X2-C interface.

Also, the radio base station DeNB1, the radio base station DeNB2 and theradio base station eNB1 are each respectively connected with the mobileswitching center MME via an S1-MME interfaces.

In such a mobile communication system, the mobile station UE isconfigured so as to establish a radio bearer between the radio basestations eNB (DeNB) and the relay nodes RN in order to perform radiocommunication.

Also, in such a mobile communication system, as illustrated by (4) ofFIG. 1, the mobile station UE is configured so as to conduct a handoverprocess between the state in which a radio bearer is established withthe relay node RN2 (the first relay node) in order to communicate viathe relay node RN2 and the radio base station DeNB2 (the radio basestation), and the state in which a radio bearer is established with therelay node RN3 (the second relay node) in order to communicate via therelay node RN2 and the radio base station DeNB2.

Additionally, in such a handover process, control signals (X2AP signals)involved in the handover process are configured so as to be transmittedand received via the radio bearer (Un interface) between the relay nodeRN2 and the radio base station DeNB2, and via the radio bearer (Uninterface) between the relay node RN3 and the radio base station DeNB2.

Note that in the present embodiment, a radio bearer (Un interface) isconfigured not to be established between the relay node RN2 and therelay node RN4.

Specifically, as illustrated in FIG. 2, as X2-C radio bearer functionsfor establishing an X2-C radio bearer with the radio base station DeNB2(Un interface), the relay node RN2 includes a physical (PHY) layerfunction, an MAC (Media Access Control) layer function provided as anupper layer function of the physical (PHY) layer function, an RLC (RadioLink Control) layer function provided as an upper layer function of theMAC layer function, and a PDCP (Packet Data Convergence Protocol) layerfunction provided as an upper layer function of the RLC layer function.

Note that the relay node RN2 may include an RRC (Radio Resource Control)layer function provided as an upper layer function of the PDCP layerfunction.

As illustrated in FIG. 2, as an upper layer function of the X2-C radiobearer functions, the relay node RN2 may include an IP layer functionconfigured so as to perform security processes between the relay nodeRN2 and the radio base station DeNB2, and may include an SCTP layerfunction configured so as to perform keep-alive processes for the X2-Cradio bearer as an upper layer function of the IP layer function.

The relay node RN2 may include an X2AP layer function configured totransmit and receive control signals involved in the handover process,as an upper layer function of the SCTP layer function.

Similarly, as X2-C radio bearer functions for establishing an X2-C radiobearer with the radio base station DeNB2 (Un interface), the relay nodeRN3 includes a physical (PHY) layer function, an MAC layer functionprovided as an upper layer function of the physical (PHY) layerfunction, an RLC layer function provided as an upper layer function ofthe MAC layer function, and a PDCP layer function provided as an upperlayer function of the RLC layer function.

Note that the relay node RN3 may include an RRC layer function providedas an upper layer function of the PDCP layer function.

As an upper layer function of the X2-C radio bearer functions, the relaynode RN3 may include an IP layer function configured so as to performsecurity processes between the relay node RN3 and the radio base stationDeNB2, and may include an SCTP layer function configured so as toperform keep-alive processes for the X2-C radio bearer as an upper layerfunction of the IP layer function.

The relay node RN3 may include an X2AP layer function configured totransmit and receive control signals involved in the handover process,as an upper layer function of the SCTP layer function.

The radio base station DeNB2 also includes an X2-C radio bearer functionfor establishing an X2-C radio bearer (Un interface) with the relay nodeRN2 and the relay node RN3.

The radio base station DeNB2 also includes an IP layer function providedas an upper layer function of the X2-C radio bearer function and thebearer function, an SCTP function provided as an upper layer function ofthe IP layer, and an X2AP layer function provided as an upper layerfunction of the SCTP layer function.

A description is given below with reference to FIG. 3 for the operationin the mobile communication system according to the present embodimentin which the mobile station UE hands over from the state in which aradio bearer has been established with the relay node RN2 in order tocommunicate via the relay node RN2 and the radio base station DeNB2, tothe state in which a radio bearer has been established with the relaynode RN3 in order to communicate via the relay node RN3 and the radiobase station DeNB2.

As illustrated in FIG. 3, the relay node RN2 manages the “UE Context” ofthe mobile station UE in step S1000, and transmits an “HO Request(handover request signal)” to the radio base station DeNB2 via the X2-Cradio bearer in step S1001 to request a handover by the mobile stationUE from the relay node RN2 to the relay node RN3.

The radio base station DeNB2, upon receiving the “HO Request” in theX2AP layer function, stores the “UE Context” of the mobile station UE instep S1002, and transfers the “HO Request” to the relay node RN3 via theX2-C radio bearer in step S1003.

The relay node RN3, upon receiving the “HO Request”, stores the “UEContext” of the mobile station UE in step S 1004, and transmits an “HORequest Ack (handover request acknowledgement signal)” to the radio basestation DeNB2 via the X2-C radio bearer in step S1005.

The radio base station DeNB2, upon receiving the “HO Request Ack” in theX2AP layer function, transfers the “HO Request Ack” to the relay nodeRN2 via the X2-C radio bearer in step S1006.

In step S1007, the relay node RN2 transmits an “HO Command (a handoverinstruction signal)” to the mobile station UE commanding a handover tothe relay node RN3 by means of the RRC layer function.

In step S1008, the mobile station UE transmits an “HO Complete (handovercompletion signal)” to the relay node RN3 by means of the RRC layerfunction.

In step S1009, the relay node RN3 transmits a “Path Switch Request (pathswitch request signal)” to the mobile switching center MME via theS1-MME interface.

In step S1010, the mobile switching center MME transmits a “Path SwitchRequest Ack (path switch request acknowledgement signal)” to the relaynode RN3 via the S1-MME interface, and also switches the single transferdestination addressed to the mobile station UE from the relay node RN2to the relay node RN3.

In step S1011, the relay node RN3 transmits a “UE Context Release” tothe radio base station DeNB2 via the X2-C radio bearer; in step S1012,the radio base station DeNB2 transfers the “UE Context Release” to therelay node RN2 via the X2-C radio bearer in the X2AP layer function, andthe relay node RN2 terminates management of the “UE Context” of themobile station UE in reaction to the “UE Context Release”.

Note that in FIG. 3, it is acceptable to interchange the relay node RN2with the relay node RN3.

As described above, the X2AP layer function in the radio base stationDeNB2 is configured so as to convert the control signal (X2AP signal)involved in the handover process between the relay node RN2 and theradio base station DeNB2, and the control signal (X2AP signal) involvedin the handover process between the relay node RN3 and the radio basestation DeNB2.

The X2AP layer function in the radio base station DeNB2 is alsoconfigured to manage such that the mobile station ID that is usedbetween the relay node RN2 and the radio base station DeNB2, and themobile station ID that is used between the relay node RN3 and the radiobase station DeNB2 are associated.

According to the mobile communication system of the present embodiment,it is possible to implement a handover process involving the relay nodesRN without performing a major renovation of the protocol stack of eachdevice used in the mobile communication system of the LTE scheme.

(Mobile communication system according to a second embodiment of thepresent invention)

A description will be provided for the mobile communication systemaccording to the second embodiment of the present invention, withreference to FIG. 4 and FIG. 5. The mobile communication systemaccording to the second embodiment of the present invention will bedescribed by focusing on the points of difference with the mobilecommunication system according to the first embodiment as describedabove.

Specifically, as illustrated in FIG. 4, as X2-C radio bearer functionsfor establishing an X2-C radio bearer with the radio base station DeNB2(Un interface), the relay node RN2 includes a physical (PHY) layerfunction, an MAC layer function provided as an upper layer function ofthe physical (PHY) layer function, an RLC layer function provided as anupper layer function of the MAC layer function, and a PDCP layerfunction provided as an upper layer function of the RLC layer function.

Note that the relay node RN2 may include an RRC layer function providedas an upper layer function of the PDCP layer function.

As illustrated in FIG. 4, relay node RN2 is configured to operate as aproxy of the RRC layer function in the mobile station UE, and may notinclude an IP layer function configured so as to perform securityprocesses between the relay node RN2 and the radio base station DeNB2 asan upper layer function of the X2-C radio bearer functions, an SCTPlayer function configured so as to perform keep-alive processes for theX2-C radio bearer, and an X2AP layer function configured so as totransmit and receive control signals involved in the handover process.

Further, the protocol stack of the radio base station DeNB2 and therelay node RN3 is the same as the protocol stack of the mobilecommunication system according to the first embodiment as illustrated inFIG. 2.

A description is given below with reference to FIG. 5 for the operationin the mobile communication system according to the present embodimentin which the mobile station UE hands over from the state in which aradio bearer has been established with the relay node RN2 in order tocommunicate via the relay node RN2 and the radio base station DeNB2, tothe state in which a radio bearer has been established with the relaynode RN3 in order to communicate via the relay node RN3 and the radiobase station DeNB2.

As illustrated in FIG. 5, the relay node RN2, upon receiving a“Measurement Report (measurement report)” from the mobile station UE instep S2000, acquires the “UE Context” of the managing mobile station UEin step S2001 in order to then transfer the “Measurement Report”, whichincludes the “UE Context” of the mobile station UE, to the radio basestation DeNB2 by means of the RRC layer function in step S2002.

The radio base station DeNB2 decides to perform a handover process ofthe mobile station UE from the relay node RN2 to the relay node RN3based on the received “Measurement Report”, and, in step S2003, storesthe “UE Context” of the mobile station UE and then, in step S2004,transmits to the relay node RN3 an “HO Request (handover requestsignal)” requesting a handover of the mobile station UE from the relaynode RN2 to the relay node RN3, via the X2-C radio bearer.

The relay node RN3, upon receiving the “HO Request”, stores the “UEContext” of the mobile station UE in step S2005, and transmits an “HORequest Ack (handover request acknowledgement signal)” to the radio basestation DeNB2 via the X2-C radio bearer in step S2006.

The radio base station DeNB2, upon receiving the “HO Request Ack”,transmits an “HO Command (handover instruction signal)” to the relaynode RN2 commanding a handover to the relay node RN3 by means of the RRClayer function in step S2007.

In step S2008, the relay node RN2 transfers the received “HO Command” tothe mobile station UE by means of the RRC layer function.

In step S2009, the mobile station UE transmits an “HO Complete (handovercompletion signal)” to the relay node RN3 by means of the RRC layerfunction.

In step S2010, the relay node RN3 transmits a “Path Switch Request (pathswitch request signal)” to the mobile switching center MME via theS1-MME interface.

In step S2011, the mobile switching center MME transmits a “Path SwitchRequest Ack (path switch request acknowledgement signal)” to the relaynode RN3 via the S1-MME interface, and also switches the single transferdestination addressed to the mobile station UE from the relay node RN2to the relay node RN3.

In step S2012, the relay node RN3 transmits a “UE Context Release” tothe radio base station DeNB2 via the X2-C radio bearer.

In step S2013, the radio base station DeNB2 transfers an “RRC ConnectionRelease” to the relay node RN2 in the RRC layer function, and then therelay node RN2 terminates management of the “UE Context” of the mobilestation UE in reaction to the “RRC Connection Release”.

(Mobile communication system according to a third embodiment of thepresent invention)

A description will be provided for the mobile communication systemaccording to the third embodiment of the present invention, withreference to FIG. 6 and FIG. 7. The mobile communication systemaccording to the third embodiment of the present invention will bedescribed by focusing on the points of difference with the mobilecommunication system according to the first embodiment as describedabove.

Specifically, as illustrated in FIG. 6, the radio base station DeNB2includes an X2-C radio bearer function for establishing an X2-C radiobearer (Un interface) with the relay node RN2 and the relay node RN3.

The radio base station DeNB2 also includes an IP layer function providedas an upper layer function of the X2-C radio bearer function, but doesnot include an SCTP function or X2AP layer function provided as upperlayer functions of the IP layer function.

Note that the protocol stack of the relay node RN2 and the relay nodeRN3 is the same as the protocol stack of the mobile communication systemaccording to the first embodiment as illustrated in FIG. 2.

A description is given below with reference to FIG. 7 for the operationin the mobile communication system according to the present embodimentin which the mobile station UE hands over from the state in which aradio bearer has been established with the relay node RN2 in order tocommunicate via the relay node RN2 and the radio base station DeNB2, tothe state in which a radio bearer has been established with the relaynode RN3 in order to communicate via the relay node RN3 and the radiobase station DeNB2.

As illustrated in FIG. 7, the relay node RN2 manages the “UE Context” ofthe mobile station UE in step S3000, and transmits an “HO Request(handover request signal)” to the radio base station DeNB2 via the X2-Cradio bearer in step S3001 to request a handover by the mobile stationUE from the relay node RN2 to the relay node RN3.

The radio base station DeNB2, upon receiving the “HO Request” in stepS3002 by means of the IP layer function, transfers the “HO Request” tothe relay node RN3 via the X2-C radio bearer in step S3003.

The relay node RN3, upon receiving the “HO Request”, stores the “UEContext” of the mobile station UE in step S3004, and transmits an “HORequest Ack (handover request acknowledgement signal)” to the radio basestation DeNB2 via the X2-C radio bearer in step S3005.

The radio base station DeNB2, upon receiving the “HO Request Ack” bymeans of the IP layer function, transfers the “HO Request Ack” to therelay node RN2 via the X2-C radio bearer in step S3006.

In step S3007, the relay node RN2 transmits an “HO Command (a handoverinstruction signal)” to the mobile station UE commanding a handover tothe relay node RN3 by means of the RRC layer function.

In step S3008, the mobile station UE transmits an “HO Complete (handovercompletion signal)” to the relay node RN3 by means of the RRC layerfunction.

In step S3009, the relay node RN3 transmits a “Path Switch Request (pathswitch request signal)” to the mobile switching center MME via theS1-MME interface.

In step S3010, the mobile switching center MME transmits a “Path SwitchRequest Ack (path switch request acknowledgement signal)” to the relaynode RN3 via the S1-MME interface, and also switches the single transferdestination addressed to the mobile station UE from the relay node RN2to the relay node RN3.

In step S3011, the relay node RN3 transmits a “UE Context Release” tothe radio base station DeNB2 via the X2-C radio bearer.

The radio base station DeNB2, upon receiving the “UE Context Release” bymeans of the I layer function in step S3012, transfers the “UE ContextRelease” to the relay node RN2 via the X2-C radio bearer in step S3013,and the relay node RN2 terminates the management of the “UE Context” ofthe mobile station UE in reaction to the “UE Context Release”.

Note that operation of the above described the mobile station UE, therelay node RN, the radio base station eNB and the mobile switchingcenter MME may be implemented by means of hardware, a software moduleexecuted by a processor, or a combination of both.

The software module may be provided in any type of storage medium suchas an RAM (Random Access Memory), a flash memory, a ROM (Read OnlyMemory), an EPROM (Erasable Programmable ROM), an EEPROM (ElectronicallyErasable and Programmable ROM), a register, a hard disk, a removabledisk, or a CD-ROM.

The storage medium is connected to the processor so that the processorcan read and write information from and to the storage medium. Also, thestorage medium may be integrated into the processor. Also, the storagemedium and the processor may be provided in an ASIC. The ASIC may beprovided in the mobile station UE, the relay node RN, the radio basestation eNB and the mobile switching center MME. Also, the storagemedium and the processor may be provided in the mobile station UE, therelay node RN, the radio base station eNB and the mobile switchingcenter MME as a discrete component.

Hereinabove, the present invention has been described in detail usingthe above embodiment; however, it is apparent to those skilled in theart that the present invention is not limited to the embodimentdescribed herein. Modifications and variations of the present inventioncan be made without departing from the spirit and scope of the presentinvention defined by the description of the scope of claims. Thus, whatis described herein is for illustrative purpose, and has no intentionwhatsoever to limit the present invention.

The invention claimed is:
 1. A mobile communication system in which afirst relay node and a radio base station are connected via a radiobearer, a second relay node and the radio base station are connected viaa radio bearer, wherein the first relay node and the second relay nodecomprise: as a radio bearer function of setting a Un (air) interfacewith the radio base station, a physical layer function; a Media AccessControl (MAC) layer function provided as an upper layer function of thephysical layer function; a Radio Link Control (RLC) layer functionprovided as an upper layer function of the MAC layer function; a PacketData Convergence Protocol (PDCP) layer function provided as an upperlayer function of the RLC layer function; and a Radio Resource Control(RRC) layer function provided as an upper layer function of the PDCPlayer function; as an upper layer function of the radio bearer function,an Internet Protocol (IP) layer function; a Stream Control TransmissionProtocol (SCTP) layer function provided as an upper layer function ofthe IP layer function; and a X2Application Protocol (X2AP) layerfunction provided as an upper layer function of the SCTP layer function;the radio base station comprises: as a radio bearer function of settinga Un interface with the first relay node and the second relay node, aphysical layer function; a MAC layer function provided as an upper layerfunction of the physical layer function; an RLC layer function providedas an upper layer function of the MAC layer function; a PDCP layerfunction provided as an upper layer function of the RLC layer function;and an RRC layer function provided as an upper layer function of thePDCP layer function; as an upper layer function of the radio bearerfunction, an IP layer function; an SCTP layer function provided as anupper layer function of the IP layer function; and an X2AP layerfunction provided as an upper layer function of the SCTP layer function,and a control signal involved in a handover process is configured to beterminated between the X2AP layer function of the first relay node andthe X2AP layer function of the radio base station, and between the X2APlayer function of the second relay node and the X2AP layer function ofthe radio base station, wherein the radio base station manages a UEcontext of the mobile station included in the control signal involved inthe handover process until the handover process is terminated.